MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI// SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 31W (YUTU) WARNING NR 03// RMKS// 1. FOR METEOROLOGISTS. 2. 6 HOUR SUMMARY AND ANALYSIS. TROPICAL STORM 31W (YUTU), LOCATED APPROXIMATELY 706 NM EAST- SOUTHEAST OF ANDERSEN AFB, HAS TRACKED WEST-NORTHWESTWARD AT 10 KNOTS OVER THE PAST SIX HOURS. ANIMATED MULTISPECTRAL SATELLITE IMAGERY SHOWS DEEP CONVECTION WITH IMPROVED SPIRAL BANDING WRAPPING AROUND A SOMEWHAT ELONGATED LOW-LEVEL CIRCULATION CENTER (LLCC). THE INITIAL POSITION IS PLACED WITH FAIR CONFIDENCE BASED ON A 212314Z METOP-A 89GHZ MICROWAVE IMAGE, WHICH IS BETWEEN THE PGTW FIX TO THE WEST AND KNES FIX TO THE EAST. THE 212316Z ASCAT SCATTEROMETER WINDS INDICATE THAT THE WESTERN PERIPHERY OF THE ELONGATED LLCC IS TOWARD THE PGTW FIX, WHEREAS THE DEEPEST CONVECTION TO THE EAST WRAPPING AROUND THE MID-LEVEL CIRCULATION IS CLOSER TO THE KNES FIX. ALL OF THIS EVIDENCE SUGGESTS THAT THE LLCC IS SOMEWHAT ELONGATED FROM THE WEST TO EAST WITH SOME SLIGHT VORTEX TILING DOWNSHEAR. TS 31W IS EXPERIENCING SOME LIGHT WESTERLY VERTICAL WIND SHEAR (10-15 KNOTS), BUT WITH EXCELLENT AND IMPROVING OUTFLOW AS THE TUTT CELL TO THE NORTHWEST GRADUALLY FILLS AND DEAMPLIFIES. SEA SURFACE TEMPERATURES REMAIN WARM (30 TO 32 DEGREES CELSIUS), AND THE SYSTEM IS EXPECTED TO TRAVERSE A FAVORABLE ENVIRONMENT THAT IS CONDUCIVE FOR INTENSIFICATION AS IT TRACKS TOWARD THE NORTHWEST AROUND THE SOUTHWESTERN PERIPHERY OF A SUBTROPICAL RIDGE (STR). 3. FORECAST REASONING. A. THE INTENSITY FORECAST WITHIN TAU 48 WAS INCREASED TO ACCOUNT FOR THE LIKELIHOOD OF RAPID INTENSIFICATION, BUT OTHERWISE, THERE IS NO CHANGE TO THE FORECAST PHILOSOPHY SINCE THE PREVIOUS PROGNOSTIC REASONING MESSAGE. B. THROUGH TAU 72, TS 31W WILL CONTINUE TRACKING TOWARD THE NORTHWEST AROUND THE STR, WITH ENVIRONMENTAL CONDITIONS REMAINING FAVORABLE FOR INTENSIFICATION. AS THE WEAK TUTT CELL TO THE NORTHWEST FILLS, POLEWARD OUTFLOW IS EXPECTED TO DRAMATICALLY IMPROVE, AND A PERIOD OF RAPID INTENSIFICATION IS LIKELY BETWEEN TAUS 12 AND 48. BY TAU 72, TS 31W WILL REACH AN INTENSITY OF AT LEAST 110 KNOTS. DYNAMIC MODEL GUIDANCE IS IN GOOD AGREEMENT THAT TS 31W WILL TRACK NORTHWESTWARD THROUGH TAU 72, SO THERE IS HIGH CONFIDENCE IN THIS PORTION OF THE JTWC FORECAST TRACK. C. BEYOND TAU 72, A WEAKNESS IN THE STR INDUCED BY AN UPPER- TROPOSPHERIC TROUGH WILL GRADUALLY TURN TS 31W SLIGHTLY MORE POLEWARD. HOWEVER, THERE IS STILL A SIGNIFICANT SPREAD IN THE DYNAMIC MODEL GUIDANCE IN THESE EXTENDED TAUS, WITH THE GFS-RELATED MODEL SUITE (AVNO, AEMN, HWRF) RECURVING THE SYSTEM TOWARD THE NORTH AWAY FROM THE MARIANAS. THE REST OF THE CONW GUIDANCE TRACKS THE SYSTEM TOWARD AND THROUGH THE NORTHERN MARIANAS, SO THE JTWC FORECAST TRACK IS SLIGHTLY WEST OF CONW. ENVIRONMENTAL CONDITIONS ARE EXPECTED TO REMAIN FAVORABLE FOR INTENSIFICATION, AND TS 31W IS FORECAST TO REACH SUPER TYPHOON INTENSITY BY THE END OF THE FORECAST PERIOD. THE FORECAST OF 135 KNOTS AT TAU 120 IS ACTUALLY SLIGHTLY LOWER THAN ICNW, SO DEPENDING ON WHETHER RAPID INTENSIFICATION OCCURS IN THE SHORT TERM, THE POSSIBILITY EXISTS THAT TS 31W WILL BECOME EVEN MORE INTENSE THAN CURRENTLY FORECAST. DUE TO THE SIGNIFICANT SPREAD IN THE MODEL GUIDANCE AT THESE EXTENDED TAUS, THERE IS LOW CONFIDENCE IN THIS PORTION OF THE JTWC FORECAST TRACK.// NNNN NNNN